Blinking Parking Brake Light. Options

[Olympic 914]

Out running errands and when leaving I noticed the brake light blinking. I do use the parking brake a lot. so I pulled it on and off a couple times, no change. The brakes feel normal. Stopped for gas and checked the fluid reservoir, its at the proper level.

Then driving home, after a couple miles the light went off. (?)

When I got home it was back on again.


I am thinking maybe a wonky parking brake switch. But will check the switch on the master also

Is the parking brake switch a Normal Open or Normal Closed?

Anyone else have this happen ? Or know of something else I should check....

[Superhawk996]

Is the parking brake switch a Normal Open or Normal Closed?

. . . know of something else I should check....

Normal open - switch closes makes ground for the bulb circuit.

Check the wiring. Runs through the seat crossmember toward tunnel. May be intermittently shorting to ground if wire is chaffed. Same principle for the brake m/c switch wiring - make sure not chaffed / shorting to ground.

[Note] there is a 3rd path on brown/white wire that comes from the seat belt flasher circuit. This is usually disconnected under the passenger seat but could be intermittently shorting on that ground wire too.

[Spoke]

@Olympic 914

Tom,

EP26 has a very low threshold for flashing and sometimes leakages in wiring can cause the EP26 to cycle all by itself.

However, you mention that the brake warning light flashes. See below schematic. If the brake warning light is flashing, then either the MC or ebrake switch is making contact. Maybe not all the time but some times.

I would start with the ebrake switch since it's easiest to get to and pull the switch out and see if you get the brake light flashing. If it still flashes, pull the wires off of the MC warning switch and see if that cures it.

[Olympic 914]

Ok, confirmed it is not the parking brake switch.

Just got it up in the air to remove the pan to access the master cylinder, but that may have to wait a day. (4th of July stuff happening)

If that is not it I will have to check the wires'

Checked that the 4-ways and turn signals function correctly.


Thanks Jerry for the wiring diagram.

[windforfun]

Are the turn signal indicator labels in the schematic correct? They look like they're flipped.

(IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/confused24.gif)

[Spoke]

Are the turn signal indicator labels in the schematic correct? They look like they're flipped.

(IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/confused24.gif)

Yes. They are correct. Has to do with alerting the driver of a burned exterior bulb. The OEM flasher connects the common connection of the indicators to 12V when bulbs are good. So the indicator for a side is grounded by going through the other side's exterior (and unlit) bulbs. If an exterior bulb is burned out, C2 will not connect to 12V; remain open circuit and both indicators will flash together.

911 models up to 1984 are connected the same way. Part of the instructions for installing EP26 when doing LEDs is to pull the tach, pull out and swap the L and R indicators.

[Olympic 914]

Switch on the master was popped. Cleaned the contacts and tested everything.

Pushed in to reset, all is good now and back together. Haven't taken it for a drive yet though.

What would cause this switch to trip? The brakes work fine, same as always. fluid level is correct. pedal solid.

A few years back I did have an ATE master go bad, the pedal would slowly go to the floor. but not leaking fluid. I assume a bad seal inside. Replaced it with another ATE unit (that is in here now) BUT the question is why didn't the light come on THEN when something was wrong and Now when nothing is wrong it does??


Inquiring minds want to know.

[porscheteck914]

Is the parking brake switch a Normal Open or Normal Closed?

. . . know of something else I should check....

Normal open - switch closes makes ground for the bulb circuit.

Check the wiring. Runs through the seat crossmember toward tunnel. May be intermittently shorting to ground if wire is chaffed. Same principle for the brake m/c switch wiring - make sure not chaffed / shorting to ground.

[Note] there is a 3rd path on brown/white wire that comes from the seat belt flasher circuit. This is usually disconnected under the passenger seat but could be intermittently shorting on that ground wire too.

I am having the same problem . So if master cyl switch is open, light in dash does not flash. All is good . If master cyl switch is sensing a problem with brake pressure it becomes closed and light flashes . Correct ??? If brakes and all wiring is good and dash light flashes that means master switch is bad ? Please help. Correct me if wrong . thanks , Paul

[Spoke]

I am having the same problem . So if master cyl switch is open, light in dash does not flash. All is good . If master cyl switch is sensing a problem with brake pressure it becomes closed and light flashes . Correct ??? If brakes and all wiring is good and dash light flashes that means master switch is bad ? Please help. Correct me if wrong . thanks , Paul

Correct on the switch:
Open = normal
Closed = Fault detected

The MC warning switch should have a reset button. I tripped mine one time when I was working on the brakes. Don't remember what caused it but it tripped during the work. Pressed the button and been good ever since.

[Superhawk996]

The master cylinder switch is triggered by a pressure differential between the hydraulic circuits.

Differential pressure allowed a small piston to move one way or another based on which side of the piston had higher pressure on it. That movement triggers the electrical switch.

If triggers again after the reset, I would take that warning seriously and would investigate what is causing it to trigger. Usually that is a sign of a failing master cylinder. It can also indicate that there is external leakage somewhere but that is not as common of a failure as a an internally leaking master cylinder due to worn seals or corrosion of the piston bore.

[dr914@autoatlanta.com]

may be the master cylinder switch

Out running errands and when leaving I noticed the brake light blinking. I do use the parking brake a lot. so I pulled it on and off a couple times, no change. The brakes feel normal. Stopped for gas and checked the fluid reservoir, its at the proper level.

Then driving home, after a couple miles the light went off. (?)

When I got home it was back on again.


I am thinking maybe a wonky parking brake switch. But will check the switch on the master also

Is the parking brake switch a Normal Open or Normal Closed?

Anyone else have this happen ? Or know of something else I should check....

[porscheteck914]

I am having the same problem . So if master cyl switch is open, light in dash does not flash. All is good . If master cyl switch is sensing a problem with brake pressure it becomes closed and light flashes . Correct ??? If brakes and all wiring is good and dash light flashes that means master switch is bad ? Please help. Correct me if wrong . thanks , Paul

Correct on the switch:
Open = normal
Closed = Fault detected

The MC warning switch should have a reset button. I tripped mine one time when I was working on the brakes. Don't remember what caused it but it tripped during the work. Pressed the button and been good ever since.

Thank you Jerry ! Reset button . Could someone send in a picture so I woild know what it looks like . -- of the reset button ....maybe that's all I need to. do. Thanks ALL .

[bkrantz]

The master cylinder switch is triggered by a pressure differential between the hydraulic circuits.

Differential pressure allowed a small piston to move one way or another based on which side of the piston had higher pressure on it. That movement triggers the electrical switch.

If triggers again after the reset, I would take that warning seriously and would investigate what is causing it to trigger. Usually that is a sign of a failing master cylinder. It can also indicate that there is external leakage somewhere but that is not as common of a failure as a an internally leaking master cylinder due to worn seals or corrosion of the piston bore.

Yup. It could mean that you have no/little front or rear braking.

[Olympic 914]

I imagine when you remove the switch you introduce air into the system.
So a total bleeding is then required.

[Superhawk996]

I imagine when you remove the switch you introduce air into the system.
So a total bleeding is then required.

Removal of the switch will not introduce air. There are seals on each side of the piston that keep brake fluid out of the switch plunger area.

If there is brake fluid present in the plunger area the seals are worn and leaking. All bets are off at that point and the master cylinder is due for replacement.

[PaIsa]

Out running errands and when leaving I noticed the brake light blinking. I do use the parking brake a lot. so I pulled it on and off a couple times, no change. The brakes feel normal. Stopped for gas and checked the fluid reservoir, its at the proper level.

Same problem here! Saw that the brake light was not going on (or blinking) when parking brake was applied so look to see if the bulb was burnt, turned out that there was no bulb!! Swapped in a bulb, started the car and it blinked with the car running and with parking brake released. I guess I will go through a similar troubleshooting exercise.

I will be replacing the speedo cable shortly so will take the opportunity to investigate any potential grounding of the parking brake switch and switch function. If nothing is found there, I will look at the Master cylinder.

[Lucky9146]

I have to believe this thread may be applicable to my 74 911 which also has a blinking brake light after a complete brake job. New everything, except the parking brake switch. (IMG:style_emoticons/default/idea.gif)
Thanks for all the tips. Always good to get new perspectives.
(IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/white914.jpg)

[Dave_Darling]

If it's blinking after a complete brake job, you need to press the reset button on the switch on the side of the master cylinder. Bleeding the brakes is enough pressure difference between the front and rear circuits to trip the switch, and it resets by pressing the button.

--DD

[Lucky9146]

@Dave_Darling

I like the sound of this "you need to press the reset button on the switch on the side of the master cylinder."

You mean there is a reset button on the side of the brake light switch? Right? Hmmm not seeing it? (IMG:style_emoticons/default/idea.gif) Not trying to be a wise guy. Don't get me wrong, I want to press a reset button so bad.
(IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/white914.jpg)

Pelican offering and switch installed 2 pole








And a glimpse of the switch on a 914 Master


Pictured on 914 is single pole, and I just looked at a 914 switch that I have and it does have a reset button.

Any other suggestions please.

[robkammer]

Having just swapped out the pressure regulator in our 74, as usual I forgot to push the button on the MC before taking the test run, and was reminded by the blinking brake warning light.The pressure switch in the Pelican picture does not seem to be the correct switch for a 914. There is definitely a button that needs to be pushed back in once you have done any brake work.
You'll have to drop the pan, and maybe pull the boot back if you have one. If that doesn't turn the light off, I'd put in a new switch unless you see brake fluid where it should not be.
Cheers